Now, let's assume, for the sake of this tutorial, that the last mod that you installed was "PM On Registration".

In the afore-mentioned "backups" directory, you'd need the file:

2010-01-26_before_PM_On_Registration_1-0-2.tar.gz

The numbers at the front of the filename are the date that the mod was installed, so they'll be different, for you.

Download that file to your desktop, or somewhere fairly empty of files and dearchive it.

It's a "gz" file.

When you dearchive it you'll be left with a "tar" file.

If you dearchive that, you'll find loads of files and directories.

Upload those files and directories to your forum, overwriting what's there, now. (It'll take a while).

When that's done, Voila! Your forum should be exactly as it was, before you installed the mod!

Next time, backup before installing mods, won't you? ;)

ahrasis:
K@, I realized this too but unfortunately I have to note that the backups is limited in the sense that it backups ONLY the Sources folder and forum root files and not other folders in the forum.

If a mod is changing for example Themes folder like css files etc, it wont restore them at all. The corrupt installation that have changed anything in the *.template.php files in that folder will not be restored using those backups. This is mainly important to note since a line of code in the template file can also caused site error.

As you have said, be a good admin and do backup before installing any mods or even themes.

I hope that may be, the Themes folder especially, will also be backed up together automatically by SMF forum software in the future.

Norv:
Actually the backup should have the Themes files. Not the images - no image, that would make it huge quite uselessly, but templates, css, languages, and scripts, yes.

kat:
It won't save custom themes, as far as I know.

If it did...

Say you had thirty themes, or so? (Some have even more)

That backups directory would be HUGE!

However, when you install a mod, it doesn't install to custom themes, anyway.

(Note that this is in the SMF v1.1.x forum's support board)

Norv:
The backups directory *is* growing huge. :D

Please keep in mind that it only saves "text" files (i.e. php, css, js, etc), so compressing them will really save some space. - and it does compress them.

In fact, it *does* save them for custom themes as well, on 1.1.11 included. Though you're right, I'm not entirely certain they should on 1.1.x... Then again, nothing stops mod makers to make their mod install on any theme of their choice (and include those specific instructions into the mod's package - even though that mostly doesn't happen in practice :)), so I guess it makes sense after all.